Pesticides Removal Using Actinomycetes and Plants

ALVAREZ, ANALÍA; FUENTES, MARÍA S.; BENIMELI, CLAUDIA S.; CUOZZO, SERGIO A.; SÁEZ, JULIANA M.; AMOROSO, MARÍA J.

Fungi as bioremediators

SPRINGER

Lugar: Tehran; Año: 2011; p. 227 - 242

Organochlorine pesticides have been used extensively all over the world for public health and agricultural purposes. Currently, their use is being phased out because of their toxicity, environmental persistence and accumulation in the food chain. Hexachlorocyclohexane (HCH) is one of the most extensively used organochlorine pesticides for both agriculture and medical purposes. Though the use of technical mixture containing eight stereoisomers was banned in several advanced countries in the 1970s, many developing countries continue to use lindane (g-HCH) for economic reasons. Thus, new sites are continuously being contaminated by g-HCH and its stereoisomers (Blais et al. 1998; Kidd et al. 2008). Although only lindane is insecticidal, HCH as a group are toxic and considered as potential carcinogens (Walker et al. 1999).For the supply of g isomer, the other stereoisomers are separated from g-HCH and dumped as waste at different spots on the production sites causing serious soil pollution (Li, 1999). HCH continues to pose a serious toxicological problem at industrial sites where post-production of lindane along with unsound disposal practices has led to serious contamination and HCH contamination continues to be global issue (Kidd et al. 2008). These compounds have moderate volatility and can be transported by air to remote locations (Galiulin et al. 2002). Therefore, a possible pathway for bioremediation of contaminated soils is the use of indigenous microorganisms. It knows that the microbial degradation of chlorinated pesticides such as HCH is usually carried out by using either pure or mixed culture systems. There have been some reports regarding aerobic degradation of g-HCH by Gram-negative bacteria like Sphingomonas (Singh et al. 2000; Kidd et al. 2008) and by the white-rot fungi Trametes hirsutus, Phanerochaete chrysosporium, Cyathus bulleri and Phanerochaete sordida (Mougin et al. 1999; Singh and Kuhad 2000). However, little information is available on the ability of organochlorine pesticide biotransformation by Gram-positive microorganisms and particularly by actinomycete species, the main group of bacteria present in soils and sediments (De Schrijver and De Mot 1999). These Gram-positive microorganisms have a great potential for biodegradation of organic and inorganic toxic compounds, and also could remove different organochlorine pesticides when other carbon sources are present in the medium as energy source (Amoroso et al. 1998; Benimeli et al. 2003). Therefore, the ability of actinomycetes to transform organochlorine pesticides has not been widely investigated, despite studies demonstrating that actinomycetes, specifically of the genus Streptomyces, have been able to oxidize, partially dechlorinate and dealkylate aldrin, DDT and herbicides like metolachlor or atrazine (Fergurson and Corte, 1997; Radosevich et al. 1995). In addition to their potential metabolic diversity, strains of Streptomyces may be well suited for soil inoculation as a consequence of their mycelial growth habit, relatively rapid rates of growth, colonization of semi-selective substrates and their ability to be genetically manipulated (Shelton et al. 1996). One additional advantage is that the vegetative hyphal mass of these microorganisms can differentiate into spores that assist in spread and persistence. Recent studies demonstrate significantly enhanced dissipation and/or mineralisation of persistent organic pollutants (such as organochlorine pesticides; Kidd et al. 2008) at the root-soil interface or rhizosphere (rhizodegradation) (Kuiper et al. 2004; Chaudhry et al. 2005; Krutz et al. 2005). This rhizosphere effect is generally attributed to an increase in microbial density, diversity and/or metabolic activity due to the release of plant root exudates, mucigel and root lysates (Curl and Truelove 1986). A summary of potential root zone carbon sources is given in Table 1. Rhizodeposits not only provide a nutrient-rich habitat for microorganisms but can potentially enhance biodegradation in different ways: they may facilitate the co-metabolic transformation of pollutants with similar structures, induce genes encoding enzymes involved in the degradation process, increase contaminant bioavailability, and/or selectively increase the number and activity of pollutant degraders in the rhizosphere (Schnoor et al. 1995; Burken and Schnoor 1998; Miya and Firestone 2001; Shaw and Burns 2003).The aim of this work was to study the bioremediation capacity of indigenous actinomycete strain, and the effect of root exudates of Zea mays on this process.